Wafer bonding is a technology used in micro-electronics fabrication, in which a first substrate carrying first devices on its surface is aligned with second devices on a surface of a second substrate for fabricating an electronic circuit. Typically, the contact is arranged in such a way that signals can be transported from at least one first device on the first substrate to at least one second device on the second substrate and vice versa. This arrangement is often referred to as a 3D wafer alignment.
Prior art systems for accomplishing such an alignment have employed optical methods, where a small hole is formed in each wafer, and a light source is used to align the holes, by passing light through holes in both wafers. However, sub-micron precision is difficult to achieve due to optical diffraction. That is, in an effort to increase precision, the holes are made smaller, but the smaller holes increase the effects of optical diffraction, making the alignment more error-prone. Furthermore, these systems require many optical sensors and a complex feedback system to control wafer position in the X, Y, and Z directions. As semiconductor technology continues the trend of miniaturization, it becomes increasingly important to achieve high-precision wafer alignment. Therefore, it is desirable to have a wafer alignment system with improved precision.